1. Field of the Invention
The invention relates to the field of sound barriers and in particular to a sound barrier capable of attenuating sound over a range of frequencies.
2. Description of Related Art
It is well known in the field of sound barriers that a single wall will reduce the sound transmitted by a source. In order to achieve the desired degree of sound attenuation, it may be necessary to use a wall so heavy or stiff as to be impractical, as for example, a wall onboard or as part of an aircraft or space vehicle, where it is desired to minimize weight. Further, the wall thickness required increases as the sound frequency decreases. Thus, especially at low frequencies, particularly thick and heavy walls are required.
One improvement to the use of a single wall is a double wall or other compound wall structure, which may have the capability of equivalent sound attenuation at lower total weight. The double or compound wall may also be stiffened, or filled with a material which absorbs or damps sound, such as a fiberglass mat or blanket; also, visco-elastic damping materials may be applied to the walls.
However, even compound walls with acoustic treatment may not be suitable. U.S. Pat. No. 4,600,078 teaches the use of acoustical resonators with a double wall partition as a means of attenuating sound. Each resonator may be designed for a specific frequency.
The use of resonators inherently imposes limitations which it is an object of the present invention to overcome.
Accordingly, it is a primary object of the present invention to provide an improved sound barrier.
It is another object of the present invention to provide a sound barrier with increased sound attenuation effectiveness without increasing the total weight thereof. It is a further object of the present invention to provide a sound barrier which conveniently attenuates sound of varying frequency, or sound of simultaneous multiple frequencies.
It is still another object of the present invention to provide a sound barrier which incorporates acoustical elements.
It is a further object of the present invention to provide a sound barrier suitable for the construction of fuselage walls for surface vehicles, marine/submarine craft, aircraft, and space vehicles.